Traffic pollution may be linked to diabetes risk

NEW YORK (Reuters Health) - People who live in areas with high levels of traffic-related air pollution may face a slightly increased risk of developing diabetes, Danish researchers conclude in a new study.

They found that people living in urban areas with high levels of nitrogen dioxide, a pollutant found in traffic exhaust, were four percent more likely to be diagnosed with diabetes than people living in neighborhoods with cleaner air.

Healthier people seemed to be in greater peril from the influence of air pollution, with diabetes risk jumping by 10 percent in physically active people and 12 percent in non-smokers.

Previous research has found that people with diabetes appear to be more vulnerable to the harmful health effects of air pollution exposure than nondiabetics.

The new study, published in the journal Diabetes Care, is the most comprehensive to date showing that air pollution may actually contribute to the development of diabetes, John Brownstein, an epidemiologist at Children's Hospital Boston, told Reuters Health.

It is also the first study to suggest that healthier individuals may be more susceptible to effects of air pollution, a finding that warrants further research, lead author Zorana J. Andersen of the Danish Cancer Society told Reuters Health in an email.

Anderson's group looked at data for nearly 52,000 residents of Denmark's two largest cities. Over the course of a decade, almost 3,000 people (5.5 percent), aged 50 to 65 at the start of the study, were diagnosed with diabetes for the first time.

The researchers also estimated outdoor nitrogen dioxide concentrations, as a proxy for vehicle exhaust in general, at people's home addresses since 1971.

In addition to having greater long-term exposure to air pollution, those diagnosed with diabetes were also more likely to be older, heavier, male and previous or current smokers.

These other traditional risk factors for diabetes continue to be the most significant indicators of the likelihood of disease, said Brownstein, though "exposure to air pollution is one factor that should be considered in a patient's risk profile."

Once such potentially confounding risk factors were accounted for in the analysis, the overall risk increase attributed to pollution by the researchers was slight, at four percent.

The link between long-term exposure to air pollution and diabetes also appeared to be greater in women in this study. This may have to do with a sex-related difference in susceptibility to air pollution or could reflect the fact that women in Denmark have historically spent more time in the home than men, Anderson speculated.

The study does not prove that air pollution itself causes the increased diabetes risk detected -- some other factor for which pollution is a flag, such as poverty, stress or other exposures, could be at work instead, for example.

Earlier this month, the same team of researchers reported that people who live in areas with high levels of traffic-related pollution also might be at a slightly increased risk of dying from stroke. (See Reuters Health story of November 16, 2011).

Considerable evidence does indicate that particles in air pollution, small enough to make their way into the bloodstream, contribute to inflammation throughout the body. Inflammation, in turn, may lead to an increased risk of heart attack, stroke, heart failure and a number of chronic diseases, including diabetes and asthma.

Air pollution has a similar effect on blood vessels as cigarette smoke, Michael Brauer, an environmental health scientist at the University of British Columbia in Canada told Reuters Health. But, unlike cigarette smoke, air pollution is something to which everyone is exposed.

"Traffic-related air pollution needs to become part of urban and transportation planning discussions," said Brauer. "Major roadways should be separated from where people live and spend time."